Research Articles

ark flour from ponderosa pine (Pinus ponderosa) was consolidated into pellets using citric acid as cross-linking agent. The pellets were evaluated for removal of toxic heavy metals from synthetic aqueous solutions. When soaked in water, pellets did not leach tannins, and they showed high adsorption capacity for Cu(II), Zn(II), Cd(II), and Ni(II) under both equilibrium and dynamic adsorption conditions. The experimental data for Cd(II) and Zn(II) showed a better fit to the Langmuir than to the Freundlich isotherm. The Cu(II) data best fit the Freundlich isotherm, and the Ni(II) data fitted both Freundlich and Langmuir isotherms equally. According to the Freundlich constant KF, adsorption capacity of pelletized bark for the metal ions in aqueous solution, pH 5.1 ± 0.2, followed the order Cd(II) > Cu(II) > Zn(II) >> Ni(II); according to the Langmuir constant b, adsorption affinity followed the order Cd(II) >> Cu(II) ≈ Zn(II) >> Ni(II). Although data from dynamic column adsorption experiments did not show a good fit to the Thomas kinetic adsorption model, estimates of sorption affinity series of the metal ions on pelletized bark derived from this model were not consistent with the series derived from the Langmuir or Freundlich isotherms and followed the order Cu(II) > Zn(II) ≈ Cd(II) > Ni(II). According to the Thomas kinetic model, the theoretical maximum amounts of metal that can be sorbed on the pelletized bark in a column at influent concentration of ≈10 mg/L and flow rate = 5 mL/min were estimated to be 57, 53, 50, and 27 mg/g for copper, zinc, cadmium, and nickel, respectively. This study demonstrated the potential for converting low-cost bark residues to value-added sorbents using starting materials and chemicals derived from renewable resources. These sorbents can be applied in the removal of toxic heavy metals from waste streams with heavy metal ion concentrations of up to 100 mg/L in the case of Cu(II).

Flax shive constitutes about 70% of the flax stem and has limited use. Because shive is a lignocellulosic by-product, it can potentially be pyrolyzed and activated to produce an activated carbon. The objective of this study was to create an activated carbon from flax shive by chemical activation in order to achieve significant binding of selected divalent cations (cadmium, calcium, copper, magnesium, nickel, zinc). Shive carbons activated by exposure to phosphoric acid and com-pressed air showed greater binding of cadmium, copper, nickel or zinc than a sulfuric acid-activated flax shive carbon reported in the literature and a commercial, wood-based carbon. Uptake of calcium from a drinking water sample by the shive carbon was similar to commercial drinking water filters that contained cation exchange resins. Magnesium removal by the shive carbon was greater than a commercial drinking water filtration carbon but less than for filters containing cation exchange resins. The results indicate that chemically activated flax shive carbon shows considerable promise as a component in industrial and residential water filtration systems for removal of divalent cations.

This work examines the precipitation of PCC – pulp composite fillers with varying crystal habits and their effects on the papermaking properties of printing and writing paper. Colloidal (c-PCC), rhombohedral (r-PCC), and scalenohedral types (s-PCC) of composite PCCs were produced and compared with commercial reference PCCs. Scanning electron micros-copy showed the c-PCC to be a high-surface-area nano-structured PCC. The rhombohedral composite was formed in clusters like a spider-web structure. Under similar experimental conditions, composite PCC was formed as individual ellipsoidal crystals and some of the particles had malformed structure, in contrast to the structured reference s-PCC. The co-precipitation and the structure of PCC significantly influence the forming, consolidation, and properties of paper, as well as its perform-ance in printing. Composite c-PCC showed the highest retention during forming. At higher filler contents, dewatering was reduced significantly with handsheets containing s- and r-PCC composite fillers. Colloidal composite hand-sheets showed the lowest tensile index and internal bond strength, while the rhombohedral composite gave the highest z-directional bond strength. Compared with the traditional reference samples containing commercial PCCs, paper with s- and r-composites had significantly higher density but similar light scattering ability. Addition of fibrillar fines to fine paper increased print rub fastness significantly in both laser and inkjet printed samples.

A long standing problem in the manufacture of wheat-straw based composites with cost-effective formaldehyde-based resins is their poor water resistance as demonstrated by their large water thickness swell. In this study, wheat straw based medium density fiberboards were manufactured using 3 resin/wax systems: a melamine-urea-formalde-hyde resin with either low or high wax content, and a phenol-formal-dehyde resin with low wax content. The flexural properties, internal bond strength, and thickness swell of the resulting composites were evaluated and compared according to ASTM methods. The three MDF compos-ites passed the requirements for MDF in interior application, except for the MDF manufactured with the aminoplastic resin and low wax content that failed to provide acceptable thickness swell. Using the phenolic resin in combination with low wax content resulted in a higher grade MDF composite, grade 120, than with the aminoplastic and high wax content. This study demonstrates that wheat straw based MDF manu-factured with cost-effective aminoplastic and phenolic resins can have flexural properties, internal bond strength and thickness swell perfor-mance above the requirements from the American National Standards Institute.

The chemical compositions of the lipophilic extractives from four clones of Eucalyptus urograndis cultivated in Brazil were studied by gas chromatography-mass spectrometry (GC-MS) before and after alkaline hydrolysis. The four E. urograndis clones showed similar amounts of dichloromethane soluble (lipophilic) extractives (0.38-0.55% w/w). The major groups of compounds identified in the lipophilic fraction of extractives consisted mainly of fatty acids (mainly palmitic linoleic and oleic acids and small amounts of a- and w-hydroxyacids), steroids (mainly b-sitosterol, b-sitostanol), followed by minor amounts long chain aliphatic alcohols, hydrocarbons and aromatic compounds. The relative abundances of these groups were similar for three of the clones with exception of the clone Ugc, which was shown to have much higher amounts of fatty acids and sterols. The high amounts of extractives found in these clones, and particularly of Ugc, when compared with other Eucalyptus species, suggests an increased risk of pitch formation during bleached pulp production.

Qualitative lignin analysis relies rather much on studies of lignin degradation products. As concerns precise quantification of lignin’s composition such studies in general have obvious limitations. Aromatic acids obtained on permanganate oxidation of pretreated lignins (cleavage of ethers and alkylation of phenolic groups) offer a possibility to estimate the amounts of differently substituted aromatic units in lignins. An equation is derived for the calculation of the gross composition of lignins based on the yields of methoxy-substituted aromatic acids obtained on permanganate oxidation of lignins with methylated phenolic groups. The equation could also be used for the calculation of the phenolic content in a lignin sample based on permanganate oxidation data, provided that such data are available for a similar lignin sample with known phenolic content. Literature data for milled wood lignin from spruce are used to exemplify the calculations.

Four commercial barrier coated boards (i.e., internally-sized uncoated board, one-side polyethylene coated board, double-side polyethylene coated board, and multilayer laminated board) were examined for biodegradation using a soil burial approach on a laboratory scale. It was observed that the base-boards were fully biodegradable in a matter of weeks or months, and the degradation process could be accelerated either by sample size modification or enrichment of the soil microbial population. Freezing pretreatment of boards or the fiber directionality of boards had no influence on the rate of degradation. The boards were also found to be recyclable following a simple procedure of re-slushing and screening. The base-boards became almost fully separated from the polyethylene coated material without any special pretreatment.

The effects of thermo-compression on the physical properties such as bulk density, mass yield, surface area, and also adsorption capacity of activated carbon were studied. The activated carbon samples were prepared from thermo-compressed and virgin fir-wood by two methods, a physical activation with CO2 and a chemical activation with KOH. A preliminary thermo-compression method seems an easy way to confer to a tender wood a bulk density almost three times larger than its initial density. Thermo-compression increased yield regardless of the mode of activation. The physical activation caused structural alteration, which enhanced the enlargement of micropores and even their degradation, leading to the formation of mesopores. Chemical activation conferred to activated carbon a heterogeneous and exclusively microporous nature. Moreover, when coupled to chemical activation, thermo-compression resulted in a satisfactory yield (23%), a high surface area (>1700 m2.g-1), and a good adsorption capacity for two model pollutants in aqueous solution: methylene blue and phenol. Activated carbon prepared from thermo-compressed wood exhibited a higher adsorption capacity for both the pollutants than did a commercial activated carbon.

The objective of this paper is to model the energy consumed in generating cellulose microfibres, 1 μm in diameter, as reinforcing agents, by refining bleached softwood kraft pulp in a PFI mill. An average initial fibre diameter of 13 μm was assumed. 125,000 revolutions in a PFI mill was found to produce a high yield of fibres 1.3 μm in diameter, and the minimum refining energy needed to reduce the fibre diameter to 1.3 μm was estimated as 1875 kJ for each 24 g charge in the PFI mill. Since elastic deformation of the fibres was found to be negligible, the size reduction was assumed to follow Rittinger’s Law. This gave a Rittinger’s constant of 28 J.m/kg for the given system. Using this value of Rittinger’s constant, the energy required to generate microfibres 1 μm in diameter was predicted as 2480 kJ for each 24 g charge in the PFI mill. It was deduced that microfibres generated in this way would cost a minimum of $2.37 per kilogram. Hence even this relatively inefficient method of grinding would not be prohibitively expensive, provided the resulting microfibres can be used as high quality reinforcements.

Industrially made kraft pulps obtained by a modified cooking process may contain 60-75 mmol/kg of hexenuronic acids (HexAs), which represents 6-7.5 kappa units. HexAs do not react with oxygen and very little of it is actually removed across the oxygen delignification stage, causing low efficiencies in the range of 25-35%. In this study, an economical evaluation of the ECF bleaching processes was carried out, having none and double-stage oxygen delignification, when applied to eucalyptus pulps of kappa varying in the range of 14-21. The bleaching processes included sequences containing specific stages for HexAs removal (Z, A/D and DHT). Results indicated that the use of oxygen delignification was not economically attractive, particularly for HexA-rich low-kappa pulps, but processes without oxygen delignification present significant environmental challenges.